I am not sure ( )there are living things on other plants or not.E_英语解答

I am not sure ( )there are living things on other plants or not.Even scientists are not sure.
A.if B.that C.whether D.where
为什么不可以选A有什么结构吗?

人气：241 ℃　时间：2020-02-03 16:19:37

解答

or not不能和if连用,只能用whether